1. Field of Invention
The present invention relates generally to a semiconductor wafer planarization system. More specifically, the invention relates to a planarization system having multiple polishing pads or webs.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to stack multiple devices on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
Two CMP systems that address these issues are described in a patent to Perlov et al. (U.S. Pat. No. 5,804,507, issued Sep. 8, 1998) and in a patent to Tolles et al. (U.S. Pat. No. 5,738,574, issued Apr. 15, 1998), both of which are hereby incorporated by reference. Perlov et al. and Tolles et al. disclose a CMP system having a planarization apparatus that is supplied wafers from cassettes located in an adjacent liquid filled bath. A transfer mechanism, or robot, facilitates the transfer of the wafers from the bath to a transfer station. From the transfer station, the wafers are loaded to one of four processing heads mounted to a carousel. The carousel moves the processing heads and wafers to various planarization stations where the wafers are planarized by moving the wafer relative to a polishing pad in the presence of a slurry or other fluid medium. The polishing pad may include an abrasive surface. Additionally, the slurry may contain both chemicals and abrasives that aid in the removal of material from the wafer. After completion of the planarization process, the wafer is returned back through the transfer station to the proper cassette located in the bath.
Another system is disclosed in a patent to Hoshizaki et al. (U.S. Pat. No. 5,908,530, issued Jun. 1, 1999) which is hereby incorporated by reference. Hoshizaki et al. teaches an apparatus for planarizing wafers wherein the wafer is subjected to uniform velocity across the wafer surface with respect to the abrasive surface. The uniform velocity across the wafer surface coupled with a multi-programable planarization pattern results in a uniform rate of material removal from the wafer surface. In addition, Hoshizaki et al. provides a number of optional routines that allow a user to fine tune material removal from the wafer.
Another system is disclosed by Sommer in a U.S. Patent Application No. 60/169,770 (filed Dec. 9, 1999 hereinafter referred to as xe2x80x9cSommer ""770xe2x80x9d) which is incorporated by reference in its entirety. Sommer ""770 describes a planarization system comprising two polishing heads for retaining wafers coupled to a drive system disposed over a single web. By polishing two wafers simultaneously on a single web, the rate of wafer throughput is enhanced.
The systems described above can generally utilize polishing pads with and without abrasive finishes. The polishing pads may be stationary or move relative to the wafer, e.g., rotationally or linearly. Additionally, abrasive slurry, di-ionized water and other fluids may be moved to the polishing pad during the processing of the wafer.
One problem common to systems utilizing webs of polishing media is the difficulty in planarizing more than one wafer having a diameter of 300 mm (approximately 11{fraction (13/16)} inches). 300 mm wafers are becoming increasingly desirable due to the ability to produce a greater number of devices on a single wafer. Currently, webs utilized as polishing pads are only available in widths up to 37 inches. These webs additionally only have a usable polishing area of about 34 inches. This conventional pad width will accommodate a polishing process that positions two 200 mm wafers side-by-side across the width of the pad when polishing, however, this pad width is insufficient to allow two 300 mm disposed side-by-side across the width of the web to travel in a polishing pattern adequate to satisfactorily planarize the wafers. As such, conventional planarization systems are limited to planarizing a single wafer across the width of the web and correspondingly, cannot obtain throughputs comparable to 200 mm systems.
Therefore, there is a need for an apparatus that provides increased throughput of 300 mm wafers in a chemical mechanical wafer planarization system.
One aspect of the present invention provides a chemical mechanical planarization system for planarizing wafers having a multiple webs. Generally, the system comprises a base, a first web disposed over the base, a second web disposed over the base, and a carrier having a first polishing head and a second polishing head. The first polishing head is movably disposed over the first web and the second polishing head is movably disposed over the second web. A drive system operably couples the carrier to the base such that the drive system moves each polishing head relative the to respective web in unison.
In an exemplary embodiment, each polishing head is moved in a polishing pattern comprising a first motion provided by a first linear motion device, and a second motion substantially perpendicular to the first motion provided by a second motion device. The system polishes at least one wafer per width of web, thus allowing polishing patterns for larger wafers, i.e., 300 mm wafers, as well as multiple smaller wafers to be accommodated.